A pulsed radar system emits a pulsed signal, or a series of pulsed signals, in a predefined direction from its antenna. The path illuminated by the radar beam, determined by the characteristics of the antenna, is referred to as the range profile. When a pulse of radio frequency (RF) energy is emitted from the transmitter and out the antenna, objects in the range profile incident to the transmission scatter a portion of the transmitted energy back in the direction of the radar, and the receiver detects the reflected signal returns. The radar processing system then determines an estimate of the range profile consisting of a plurality of range bins. Traditionally, in a pulsed system, the time delay between the transmission and reception of the radar signal determines the range to the object and the length of the pulse emitted pulse determines range resolution. The range corresponds to the distance from the radar system, and the range resolution corresponds to the ability to distinguish between objects in range.
The emitted radar signal waveforms are becoming increasingly more complex in an effort to reduce transmission power while improving sensitivity, accuracy, and resolution. One method is to emit a single pulse defined by a variable frequency, referred to as a frequency modulated or pulse compression waveform which in combination with a matched pulse compression filter at the receiver will significantly improve the signal to noise ratio (SNR) by allowing for longer pulses to be emitted while keeping range resolution reasonably high and transmit power low. Another improvement is to emit a series of single frequency sub-pulses, referred to as a pulse-train, over a relatively longer predefined time period. The returns from these sub-pulses can also be combined to improve SNR. However, if the center frequencies of the sub-pulses within the pulse-train have been intelligently stepped, the returns can be combined to increase the effective bandwidth of the radar, resulting in an increased range resolution. The latter is referred to as a stepped frequency waveform or stepped frequency pulse-train. Yet another improvement is to combine the stepped frequency and pulse compression methods by emitting a series of pulses defined by a variable frequency and stepped center frequencies over a relatively longer predefined time period, referred to as a pulse compressed stepped frequency pulse-train or waveform.
Unfortunately, with the improvements in detection sensitivity and range resolution, any pulse compression method adds undesirable artifacts to the estimated range profile. These artifacts are generally referred to as range sidelobes as they appear as returns up-range and down-range of true objects in the estimated range profile. For stepped frequency, the range sidelobes are called ambiguous peaks, and typically a small number of these ambiguous peaks result when conventional stepped frequency pulse-trains and processing methods are employed. When pulse compressed stepped frequency pulse-trains are used, the pulse compression and stepped frequency range sidelobe artifacts combine which results in the generation of many ambiguous peaks over up-range and down-range for distances equal to the uncompressed pulse length. Thus, the radar display is cluttered and it becomes more difficult to discriminate true object returns from signal processing artifacts, particularly as the complexity of the range profile increases. Therefore, it is desirable to minimize ambiguous peaks.